The invention relates to the actuation of heavy-duty disc brakes, such as truck disc brakes, by pneumatic means. In the past it has not been practical to provide a purely pneumatic actuation system for truck disc brakes because of the large forces needed to be applied to provide sufficient braking, and because of the restraints on the size and disposition of such brake actuators when placed on a vehicle. Purely pneumatic actuation has many advantages, however. Since no special reservoir of fluid is necessary, fluid leakage is not nearly as important as in hydraulic systems, and much less often results in brake failure. Also maintenance needs are greatly reduced with purely pneumatic operating means, and they are less expensive to build.
Despite the many advantages of purely pneumatic operation, prior art heavy-duty truck disc brake actuators have been practically confined to hydraulic operation. Typical prior art fluid actuating means for disc brakes are shown in U.S. Pat. Nos. 2,915,146, 3,036,869 and 3,108,658. Hydraulic actuation has been required in such an environment because since the disc brake assembly must be mounted on an axle there is not enough room to provide for a pneumatic piston of large enough area to adequately operate heavy-duty disc brakes while still providing an assembly of proper size to be disposed on a truck axle. U.S. Pat. No. 3,680,666 suggests pneumatic actuation of a motor disc brake, but such an actuator has not found practical application in heavy-duty trucks in meeting the braking standards for trucks (particularly "low-boy" trucks) set forth in the Federal Regulations of Title 49, Chapter V, Part 571 -- Federal Motor Vehicle Safety Standards, Air Brake Systems Standard and Hydraulic Brake Systems, as set forth in the Federal Register, Vol. 39, No. 97, May 17, 1974 and Vol. 37, No. 172, Sept. 2, 1972. According to the present invention, these standards can be met even with only pneumatic actuation of the brakes.
According to the present invention, a purely pneumatic actuator is provided with a heavy-duty disc brake assembly. Said actuator preferably comprises a first annular piston adapted to be disposed around a truck axle and having a pressurized air inlet on one side thereof, a vent in the cylinder behind the first piston, a second annular piston operatively connected to the first annular piston, an air inlet to one side of said piston being provided through a hollow member operatively connecting the first annular piston to the second annular piston, and said second piston being adapted to be disposed in operative engagement with discs of a heavy duty disc brake assembly. In this way, the effective area of a piston actuator for the disc brake assembly is greatly increased while the size of the assembly is increased only slightly, and that increase is along the length of an axle on which the brake assembly will be disposed rather than the width. While dual pistons per se have been known -- see U.S. Pat. Nos. 2,956,549 and 2,983,256, for example -- the combination of purely pneumatically operated annular dual pistons and a disc brake assembly, or the advantageous results achieved thereby, have not been known in the prior art.
Another exemplary pneumatic only actuating system comprising a single piston disc brake actuator biased closed by a spring and held open by air pressure and moved into positive braking position by air pressure, is also disclosed.
According to a preferred form of the invention, the pneumatic actuator is disposed on an improved self-contained oil-cooled heavy-duty disc brake assembly as is described in the parent application. The improved cooled disc brake assembly comprises a plurality of rotors having grooves on the surface thereof and a plurality of stators having passageways interiorly thereof, whereby a circulatory path of oil within the disc brake casing is established. The side portions of the casing of the assembly have heat-exchanging means formed thereon whereby oil from the casing is splattered on the casing side walls responsive to the centrifugal force of the rotors and quickly cooled. A self-pumping action is produced by the rotors -- increased by the grooves formed in the surface thereof -- and combined with the heat-exchanging means on the casing provides for self-contained cooling means for the disc brakes. The casing is provided with much less oil than the capacity thereof -- preferably about one-third the oil it could contain -- the oil being frothed during operation of the assembly and a thin layer of oil always being provided between the rotors and stators, whereby the life of the assembly is greatly extended over prior art devices.
It is a primary object of the present invention to provide an improved heavy-duty disc brake assembly with purely pneumatic actuation thereof. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.